Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains to the use of beams of laser light to measure the position, direction or velocity of a circular rotating device (such as a shaft) or of a linear motion device (such as an x, y table). The laser beams reflect off the encoded surface of a specially prepared disk or strip (similar to the commonly used polycarbonate disk with xe2x80x9cpitsxe2x80x9d and xe2x80x9clandsxe2x80x9d used to encode audio, computer data, or video information) for the purpose of very high accuracy measurement of the position, velocity, and direction of a rotating or linear motion device to which the disk or strip is attached.
2. Description of the Background Art
There are a variety of devices that have been, and which are currently used, for measuring the rotational position and direction of a rotating body, or the position and direction of a linear device such as an x, y table. These include, without limitation, potentiometers, optical encoders based upon radial lines scribed on a disk, optical encoders based upon bar code technology, encoders based upon on a magnetic disk, and other devices. Most of these devices are of limited resolution or have other limitations such as very high cost or large size.
Presently, there are no devices that provide a high degree of accuracy, at a low cost, in a reasonably sized package. This invention satisfies the need for high resolution and low cost without sacrificing accuracy.
The present invention is an apparatus and method for the precision measurement, in real time, of the position and direction of a rotating or linear moving body. Specifically, the invention pertains to a specific pattern and technique for reading such pattern so as to determine not only the number of markings, but also the direction of movement as the markings pass through the focal points of a split laser beam. Although this invention is not limited to a single laser beam that is split into multiple beams by some means (e.g., a diffraction grating), it is possible that multiple laser beams and/or other means for laser beam splitting could be utilized in a similar manner to achieve comparable results. However, the most common and economically feasible type of laser beam system to use for this invention is the 3-beam type used in standard xe2x80x9cCDxe2x80x9d players (FIG. 1).
In conventional CD use, the three beams are used for two separate purposes. The center beam is used to read the information from the disk which is encoded in the form of a digital code impressed into the disk such that the laser light is alternately scattered away from, and reflected back, into the laser unit as each impressed mark, and unimpressed space, goes by. These impressions are generally referred to as xe2x80x9cpitsxe2x80x9d, and the unmarked space around them is generally referred to as a xe2x80x9clandxe2x80x9d, or xe2x80x9clandsxe2x80x9d. The side beams, or xe2x80x9csatellite spotsxe2x80x9d as they are known, are used together to keep the main beam centered over the line of pits which encode the information. None of the encoded information is read by the satellite spots, only the average intensity of each reflected satellite beam is used: the average intensity increases if the laser is off-centered (relative to the centerline of a row of pits being read) towards a particular satellite beam, and decreases when the laser is off-centered toward the other satellite beam.
In contrast, the subject invention utilizes the amplified signal from all three beams and then digitizes these before inputting them to a unique digital counting circuit. The need for the tracking function normally performed by the satellite beams is eliminated by the design of the information pattern, and all three beams are used to read in information about every pit and land that passes beneath them.
The method of the invention comprises, in general terms, the steps of providing a position measurement pattern 3 (FIG. 2) on a disk or strip encoded with xe2x80x9cpitsxe2x80x9d 4 and xe2x80x9clandsxe2x80x9d 5 (FIG. 2), providing a suitably positioned position read head 1 (FIG. 1) with three lasers that produce laser beams 100 that pass through a diffraction grating 102 and a focus lens 104 to yield three focal spots 2(a), 2(b), 2(c) (FIG. 1) for reading the position measurement pattern 3, positioning or orienting the position read head 1 so that the relative spacing of the three laser focal spots 2 from the position read head 1 is a non-integral multiple of the spacing between the rows 6 (FIG. 2) of pits 4 and lands 5 of the position measurement pattern 3 such that the outputs from the reflected laser focus spots 2 are fully differentiated, communicating the outputs to converting means, and converting the outputs to position count, direction and velocity information.
The object of the invention is to provide an apparatus and method for accurately measuring position, direction and velocity in a rotating or linear moving object. Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.